NASA Just Fired Voyager 1’s Thrusters For the First Time in 37 Years

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Before Cassini or Galileo, there were the Voyager probes. Launched in August and September of 1977, both Voyager 1 and Voyager 2 continue to communicate with Earth via the Deep Space Network. Voyager 1 is farther from Earth than Voyager 2, due to differences in their missions and trajectories, at an estimated 141 AU from Earth (1 AU is the distance between Earth and the sun). On Friday, NASA engineers were able to successfully fire Voyager 1’s backup thrusters — for the first time in 37 years.

These small backup thrusters use hydrazine propellant and could be vital to extending Voyager 1’s mission. Keeping a communication link open to a space probe that’s now over 13 billion miles away from Earth isn’t easy, and it requires precise adjustments to the spacecraft’s orientation. Unfortunately, since 2014, NASA has noticed that the primary thrusters on Voyager were burning more and more hydrazine to perform the same course corrections. With the probe billions of miles away, there’s no opportunity to pull it over and look under the proverbial hood.

NASA describes the difference between the traditional engines and the attitude control thrusters as follows:

In the early days of the mission, Voyager 1 flew by Jupiter, Saturn, and important moons of each. To accurately fly by and point the spacecraft’s instruments at a smorgasbord of targets, engineers used “trajectory correction maneuver,” or TCM, thrusters that are identical in size and functionality to the attitude control thrusters, and are located on the back side of the spacecraft. But because Voyager 1’s last planetary encounter was Saturn, the Voyager team hadn’t needed to use the TCM thrusters since November 8, 1980. Back then, the TCM thrusters were used in a more continuous firing mode; they had never been used in the brief bursts necessary to orient the spacecraft.

But all the thrusters are the same model, MR-103, and they all draw propellant from the same sources. With that in mind, NASA decided to fire the older thrusters up and see if they could take over the attitude control adjustments. It takes 19 hours, 35 minutes for information to reach Voyager 1 and another 19 hours, 35 minutes for it to report home, so NASA didn’t get the results of the data immediately. We now know, however, that the adjustment worked perfectly, and it should allow Voyager 1 to keep communicating with Earth for a few more years.

The famous “Pale Blue Dot” image. Earth — every single one of us — is the pale dot roughly halfway down the brown band on the right.

The long-term trajectory of the Voyager mission still ends just one way. The radioisotope thermoelectric generators on Voyager provided 470W of power when the craft launched, but the half-life of the plutonium-238 the craft uses is 87.7 years. As of today, Voyager 1 has 72.76 percent of its plutonium-238 still in operation. By 2018, the probe’s Digital Tape Recorder will no longer have enough power to operate. Scientific instruments will shut down by 2020, and by 2025 or 2030, the spacecraft will no longer produce enough energy to power any instrument. Using the old TCM thrusters will buy scientists some additional time to gather data as Voyager continues to explore interstellar space.